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  • [♪ INTRO]

  • From ancient times to today, volcanoes have destroyed and threatened

  • countless civilizations and cities.

  • And even though we have some ways of monitoring and predicting

  • their activity, we still don't have a surefire way to tell

  • when a volcano will erupt.

  • And yet, nearly one in ten people lives within 100 kilometers

  • of an active volcano.

  • So, in search of more reliable ways to monitor volcanic activity,

  • some scientists have started looking at volcanoes' music.

  • You might not think of volcanoes as especially musical,

  • but they actually do generate sound.

  • It's just infrasound, whose frequency is below the threshold of human hearing.

  • These sound waves can come from different phenomena, like gas

  • getting pushed out of vents or out through the surface of a lava lake.

  • And that moving air acts kind of like air moving through

  • a wind instrument: It makes different sounds based on

  • the structure it's passing through.

  • Just like a horn's sound changes based on the shape and flare

  • of the bell, a volcano's sound can change depending on the shape

  • and depth of its crater.

  • For instance, a volcano with a deep crater might produce a deep sound,

  • while a volcano with a shallow crater would produce a higher-pitched sound.

  • Meanwhile, narrow craters also resonate for longer periods of time,

  • while wide, dish-like craters might not even resonate at all.

  • And finally, the flare of the crater's rim changes the sound's timbre,

  • which you can think of as the color of the sound.

  • It's like how a flute and oboe sound different even when they're

  • playing the same note.

  • The same applies to volcanoes.

  • And all this information can be useful.

  • Since these sounds are so tied to the volcano's shape,

  • they can change anytime the volcano changes shape.

  • Which is not uncommonespecially when a volcano is getting ready to erupt.

  • It all begins when the pressure of magma starts mounting beneath the surface.

  • This causes lots of little earthquakes around the volcano

  • that can shift around rocks and other geological features.

  • The pressure can also make crater walls change their shape,

  • kind of like how a balloon's shape changes as it inflates.

  • Eventually, those crater walls can even fracture.

  • On top of that, if there's a lava lake within the crater,

  • the mounting pressure can cause it to rise.

  • So, before a volcano erupts, the entire internal structure

  • of the crater can be rearranged.

  • And all of this changes the volcano's sound.

  • One recent example of this happened in Chile in 2015.

  • On March 3 of that year, Chile's Villarrica volcano erupted.

  • It spewed lava and ash up to a kilometer up in the air for

  • about 20 minutesand then it all went quiet.

  • As far as eruptions go, it wasn't so remarkable.

  • Some property was damaged, but no one died, and the volcano

  • has been quiet since.

  • But the Villarrica eruption is important because it's one of

  • the few cases where a volcano's sound was being monitored

  • right before the eruption.

  • And scientists actually observed a shift in Villarrica's sound

  • on March 1, 2015, two days before the eruption.

  • For one, the frequency of the sounds increased,

  • so they became slightly higher-pitched.

  • The sound waves also got broader, marking a change

  • in the timbre of the sound.

  • And finally, the volcano lost its resonance.

  • Before March 1, Villarrica's sound was reverberating in the crater,

  • which is shaped like an upside-down funnel.

  • But after March 1, those reverberations stopped.

  • That told researchers that something had changedsomething inside

  • the volcano was damping the sounds.

  • And by the next day, new infrasound readings suggested that

  • the lava lake, which was normally deep inside the funnel,

  • had actually risen to nearly the rim of the crater.

  • The next day, it exploded.

  • At the time, scientists didn't realize that they had been listening

  • to evidence of an eruption about to happen.

  • They only put all the pieces together after the fact.

  • But now, scientists are looking at how they might be able to use

  • data like this to predict eruptions in other,

  • possibly more dangerous volcanoes.

  • It's tricky because there's nonormalvolcano sound.

  • Every volcano has its own sound, so the only way to tell

  • if something is off is to detect a change.

  • And even the type of change is different from one volcano to the next.

  • But by researching volcanoes for a long time, scientists

  • can learn what different volcanoes sound like so they know

  • a change when they hear one.

  • No matter what, it's unlikely that this technique will

  • completely replace traditional methods of monitoring volcanoes,

  • but it's still exciting.

  • This is one more tool that we can use to protect ourselves

  • against dangerous volcanic eruptions.

  • And there's something kind of beautiful about the fact that

  • we can do that with volcano music.

  • Thanks for watching this episode of SciShow!

  • And if you want to learn more about volcanoes,

  • you might enjoy our episode about the biggest eruptions

  • we've witnessed in our history.

  • You can watch that one right after this!

  • [♪ OUTRO]

[♪ INTRO]

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How Volcanoes’ Music Could Help Us Predict Them

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    joey joey posted on 2021/05/19
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